1. Field of the Invention
The present invention relates to a wiring material for a flexible printed circuit (FPC) and the like and a for fabricating the wiring material as well as a secondary battery device and an electronic equipment using the same.
2. Description of the Related Art
As to the internal wirings to be used in automobiles, large electronic equipment, large mechatronics equipment or the like, it has been conventionally easy to ensure a sufficient wiring space because a casing therefor is large. It has therefore been possible to respond to complex wiring by using a wire harness with a plurality of cables bundled together. On the other hand, in small electronic equipment or small mechatronics equipment, the wiring space is required to be minimized in order to provide a plurality of functions in a small casing therefor. Therefore, a small film wiring material such as a flexible printed circuit (FPC) has been used for the internal wiring in such small equipment.
In recent years, even in the automotive applications, or the large mechatronics equipment, the equipment configuration with a size equal to or smaller than the conventional device has been required as well as the function enhancement. As a result, such a film wiring material as that used in the small electronic equipment or the mechatronics equipment has been required as the wiring in large equipment.
For example, a lithium ion secondary battery module to be mounted on an electric vehicle or a hybrid vehicle has such a structure that a plurality of single-battery cells are placed therein, and electrode terminals of the adjacent battery cells are connected each other by a connecting member such as a bus bar or the like. When the lithium ion secondary battery is excessively charged, overheat may occur. Further, when the lithium ion secondary battery is excessively discharged, the charging or discharging function may be lowered due to melting of the electrode material. It is therefore necessary to control voltage with very high accuracy of the order of several dozen of mV. Accordingly, each bus bar to be connected to each cell is connected to a control circuit and a protection circuit via a wiring material for monitoring the potential of each electrode.
Based on the size of the secondary battery module, the wiring material for voltage monitoring has a length of about 0.5 to 1 m. Further, because the wiring distances from the circuit board to respective bus bars are different, the wiring material has a plurality of conductors and an arbitrary wiring pattern in which the conductors are branched from the bundle of the plurality of conductors.
Because of the demand for miniaturization and high capacity of the lithium ion secondary battery, the number of battery cells and the number of the wiring materials are increased, while the area occupied by the wiring material is required to be reduced. Further, since the wiring of arbitrary pattern is required, the FPC or the like is used for the wiring material. The use of the thin wiring material such as FPC allows reducing the area occupied by the wiring material. Further, it is possible to prevent incorrect wiring during battery module assembly, or simplify the positioning work of the bus bar and the wiring material for the connection by forming the pattern shape in advance so as to conform to the position of each bus bar.
Also, for example, in a digital multifunction printer with copying machine, scanner, and the like combined together, it is necessary to provide wiring between a control circuit and a movable part such as a scanner reading mechanism, etc. in addition to the wiring in the apparatus. In the wiring material, the wiring length may exceed 1 m in particular when compatible with A0 size (84.1 cm×118.9 cm). Also, the wiring with the movable part side control circuit such as scanner head or ink-jet head is constituted from a branch portion to branch to the control circuit and a lengthy straight portion for a margin of the movable range. Therefore, as a wiring material of the digital multifunction printer, FPC or the like which is capable of arbitrary pattern wiring is used, similarly to the wiring material for voltage monitoring mentioned above.
The FPC, which is one example of the wiring material, is produced by a process of forming a wiring pattern by photolithography on a film base material with a copper foil bonded to a polyimide film which is a covering member, and removing an unnecessary copper portion by etching.
The FPC wastes much copper material due to the copper foil etching for the conductor pattern formation. Further, materials (photoresist, developer, washing solution, etc.) other than the etching agent are required. In particular, in the case of fabricating the wiring material for the voltage monitoring or the digital multifunction printer, the simpler such a structure that the wiring pattern is not complex and dense as in an electronic circuit, and the lengthy conductors are branched, the more the waste material is produced, resulting in an increase in cost.
Further, conventional wiring materials have been mainly used for forming the circuit of several cm square. However, the wiring material for the voltage monitoring or the digital multifunction printer has a length of about 0.5 to 1 m, or longer, existing photolithographic apparatus cannot be used for such a wiring material. Therefore, it is necessary to increase the size of the photolithographic apparatus, and the cost of producing the wiring material is therefore further increased. Because of the use of the copper foil, the FPC is very thin in conductor thickness, and increases in conductor resistance when it comes to increasing the size as described above.
A flat harness (wiring material) disclosed by JP-A-2002-157924 comprises copper wires each having a circular cross section that are laid on the same plane along a predetermined wiring pattern and covered with an insulating film from both sides. This flat harness can be produced without including any etching step.
A flat harness disclosed by JP-A-2002-203431 comprises a ribbon cable as a first flat cable, and a FPC as a second flat cable that is connected via a connecting portion to an intermediate position on the first flat cable, wherein conductors of the first flat cable, and conductors of the second flat cable are partially and electrically connected each other. According to this configuration, the flat harness without any large size FPC is provided by using the FPC in only the second flat cable, i.e., the portion branched from the first flat cable.